The objective of this project is to evaluate the technical feasibility of novel low impedance stimulating electrodes. The power consumption of implanted stimulators is dependent on the impedance of the electrode- tissue interface. Power consumption requires larger implanted packages to accommodate appropriate batteries, and finite battery lifetimes require surgical replacement of devices. Reductions in electrode impedance will reduce power consumption leading to prolonged battery life and/or smaller implant packages. We will develop and evaluate novel high-perimeter electrodes designed to exploit the non-uniform distribution of current density on the electrode surface. Electrodes with increased perimeter are intended to enhance the "edge effect"; the current density on the electrode surface is higher toward the perimeter of the electrode, and a more pronounced edge effect is expected to lower the electrode impedance. We will evaluate the performance of electrodes with an increased perimeter in three domains. First, we will make in vitro measurements of the impedance of across a spectrum of geometries designed in increase the electrode perimeter. These data will be used to test the hypothesis that increasing the electrode perimeter decreases electrode impedance and to inform subsequent electrode designs. Second, the electrode geometry can affect the pattern of neural excitation generated in the surrounding tissue, and we will quantify the patterns of neuronal excitation generated by high-perimeter electrode geometries and compare these to patterns generated by conventional electrodes. Third, the electrode geometry can affect the spatial distribution of current density over the electrode surface, an important factor in stimulation induced neural damage and electrode corrosion. We will conduct in vitro pulse testing of electrode corrosion, and quantify the effects of increasing the perimeter on the magnitude and distribution of current density across the electrode surface to assess the propensity to cause tissue damage. The outcome of these studies will be a comprehensive analytical and in vitro assessment of the technical feasibility of a new class of low impedance stimulating electrodes, and will provide the foundation for subsequent chronic in vivo testing of electrode safety and efficacy. The objective of this project is to design and analyze more efficient electrodes for use in electrical stimulation of the nervous system to treat neurological disease or injury. These electrodes will increase the lifetime of battery-powered implantable electrical stimulators. This will reduce the risks and costs associated with surgical replacement of implanted stimulators due to depletion of the batteries. [unreadable] [unreadable]